A projector apparatus requires uniform image illumination with sufficient color rendering properties to a rectangle screen. Therefore, a lamp in which 0.15 mg/mm3 or more of mercury is enclosed so as to obtain high mercury vapor pressure is used as a light source. Such a lamp is disclosed in Japanese laid open patent No. 2008-282554.
Recently, a device increases the applied electric power to the lamp and the operating gas-pressure by increasing mercury quantity is increased, for high output. As a result, the temperature of the electrode during operation is progressively increased. As a crystal grain of an electrode consisting of tungsten is grown the boundaries between crystal grains tends to decrease.
In this way, when the number of crystal grain boundaries is decreased, the electrode is broken by outside vibrations. Furthermore, in the lamp of alternative current operating, the electrode is easily broken because the electrode vibrates intensely by intense of the polarity inversion.